Tim, one thing I wasn't clear on at the workshop was what the time frame over which MSL would have the 30% to 50% duty cycle. At some times it seemed they were talking about lengthy hibernation (several months of inactivity), at other times it seemed they were talking about limited operations within a sol (needing to allow time for the rover to warm up, like a lizard in the sun as one person put it). Which one was it, or was it both?

--Emily

My understanding is that immediately upon landing at a one of the high southern latitude sites, the rover would enter hibernation and not do anything for a month or more. This is different than the situation of Spirit at Gusev, where although the rover was not moving during the winter, it was still acquiring imagery, APXS, Mini-TES, and MB data from its site.

Then, after hibernating for that extended period at the beginning of the mission, MSL would then be allowed operate on a reduced duty cycle.

About MSL's hibernation, I thought waste heat from the rover's RTG was to be transferred to a circulating fluid that would keep MSL critical systems warm at all times. Is the temperature of the southern sites too low even for this heating system, or am I in error about having active heating onboard?

In my humble opinion, the phyllosilicates are a number one priority...They may have been formed as early as at the very end of the LHB, but these clays were formed before sulphuric acids began pouring out of the interior and the entire outer surface of the planet was coated with sulphates...There seems to be precious little of this phyllosilicate material exposed on the surface. The question is, was there not much to begin with? Or was it more ubiquitous but now has been covered with lavas and/or coated with basaltic dust cemented together by sulphate salts? Investigations of the clays, and of the contact between them and the surrounding terrains, will go a long way towards painting a picture of very early conditions on Mars.-the other Doug

Other Doug - Great insights. Actually, the phyllosilicates may have formed as a RESULT of (that is, at the height of) the LHB - that period may well have been the warmest, wettest, most energy-rich time in martian history. (Remember, unequivocal signs of life appeared on Earth shortly after the end of its own LHB, other evidence of which has since been largely erased.) A life-hostile late episode of "sulfuric acids pouring out of the interior" is only one possible interpretation of the sulfate-rich surface of Mars, one that I consider rather unlikely. Others include weathering of igneous sulfides excavated by impacts (my "mine dump" modification of Roger Burns' gossan suggestion), and/or acid sulfate condensation/redistribution by impacts followed by the inability of frost or snow to leach these sulfates away from the surface (chlorides being much easier to leach, although some appear to have survived). The result was called sulfate duricrust back in Viking days and blamed on capillarity; effloresecent sulfate crusts on mine dumps form similarly. Later impacts (those occurring at the tail end of the LHB, after Mars had already seriously cooled down, or afterwards) may well have covered up many of the early clays (in addition to areas covered by late volcanism and wind). That at least is one interpretation of the impact deposits (if that's what they are) that appear to cover clay-rich sediments at both Meridiani and Gusev.

Phyllosilicates (clays) are excellent at absorping organic molecules, and I agree with you that fresh exposures of clays (as verified by CRISM and OMEGA) should therefore be priority number 1 for astrobiology (and for the MSL). I merely hypothesize that "very early conditions on Mars" (insofar as we can know them) were clearly dominated by impact cratering of the LHB, and much that we see today can still be attributed to that episode, either directly (e.g., craters and their distal deposits) or indirectly (e.g., impact-related ephemeral climate change; impact erosion of atmosphere). Whether or not life arose during those exciting times on Mars (as it may well have on Earth) remains to be determined. My personal favorite target for astrobiology might be rocks near the throat of a Tharsis volcano. Three billion years of near-constant heat, moisture, and chemical nutrients potentially could have provided a life-friendly environment impossible on Earth owing to plate tectonic movements. Of course, MSL is hardly going to land on top of a big volcano if it can help it.

My understanding is that immediately upon landing at a one of the high southern latitude sites, the rover would enter hibernation and not do anything for a month or more. This is different than the situation of Spirit at Gusev, where although the rover was not moving during the winter, it was still acquiring imagery, APXS, Mini-TES, and MB data from its site.

Then, after hibernating for that extended period at the beginning of the mission, MSL would then be allowed operate on a reduced duty cycle.

I think that the need to hibernate for one month or more rules out most Southern sites. My reason for saying this is that any probe sitting on Mars in the depths of Winter could fail at any time due to the expansion and contraction of solder joints.

One common thread running through MER briefings is that they concentrate on what Spirit and Opportunity will achieve in the next month or two. There seems to be a healthy acceptance that no rover can be presumed to carry on working for longer than a month or two in the very tough conditions on Mars.

I think that the need to hibernate for one month or more rules out most Southern sites. My reason for saying this is that any probe sitting on Mars in the depths of Winter could fail at any time due to the expansion and contraction of solder joints.

Not a rover which is kept warm by a big lump of plutonium, though. External hardware is being designed to last for a minimum of one martian year of thermal cycles.

The hibernation may rule out southern sites because no one will want to hibernate that much, but it's not because of solder joint lifetime.

--------------------

Disclaimer: This post is based on public information only. Any opinions are my own.

MSL has always had a 50% duty cycle. The RTG doesn't have enough power to permit constant roving. Anyways, roving in the dark is not a good thing to do and it would require more power than roving during the day. I haven't seen anything on a hibernation period at this point. I will make some inquires.

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